1. Field of the Invention
The present invention relates to gas catalytic heaters in general and more particularly to a novel and improved system for uniformly dispersing a combustible gas or fuel within a catalytic heater.
2. Description of the Prior Art
In any catalytic heater, heat is produced when a gaseous fuel is brought into contact with a catalyst in the presence of air containing a normal level of oxygen. Typically, the fuels are natural gas, propane and butane, for example.
Generally, the combustible gas or fuel is fed through the bottom of the catalytic heater and is dispersed at atmospheric pressure into contact with a porous active layer. This layer contains a catalyst which may be platinum, for example. Oxygen from the atmosphere enters the porous catalytic layer and reacts with the gaseous fuel, promoted by the catalyst. This reaction releases the BTU content in the fuel in the form of radiant energy.
Catalytic heaters are therefore used as a source for infrared heat. The chemical reaction that occurs during the oxidation reduction process produces temperatures within the catalyst of from about 500 to 1000 degrees Fahrenheit (F.). The by-products of the reaction include carbon dioxide and water vapor. The temperature at the surface of the catalytic heater is dependent upon the rate at which the fuel gas is introduced to the catalyst. The surface of the heater is typically rectangular or circular and ranges from about one square foot to about 10 square feet. The volume of gas delivered to the catalytic surface may range from about 2 to 6 cubic feet of gas per hour per square foot.
The catalytic heaters that are commercially available today display a reasonably even or uniform distribution of temperature at the maximum rated input of 6 cubic feet of gas per hour per square foot. This will produce a reaction temperature on the heater surface of from about 750 to about 800 degrees Fahrenheit (F.). However, when operating at the lower flow rates, that is, about 2 cubic feet of gas per hour per square foot, the temperature distribution across the heater surface will vary from about 200 to about 800 degrees Fahrenheit (F.). This poses many problems particularly when the heaters are used for heating flat areas. The catalytic heaters develop hot and cold spots across the heating surface and produce an uneven heating profile to the object being heated. As a consequence, process control is very poor and efficiency is reduced.
Another disadvantage of commercially available catalytic heaters is that some of the combustible gas or fuel is left unreacted by the catalyst and escapes through the heater into the atmosphere. This phenomenon is referred to as "methane slippage" and is expressed as a percentage of the input BTU/hour. Tests have shown that commercial catalytic heaters exhibit methane slip rates of up to as high as 25 percent. Typical operating levels are about 15 percent of the input BTU/hour rate.
It is therefore an important object of the invention to provide a gas catalytic heater having an improved temperature distribution over the working surface or face of the heater.
Another more specific object of the invention is to provide a gas catalytic heater in which the combustible gas or fuel is distributed more evenly or uniformly to the porous catalytically active layer of the heater.
Still another object of the invention is to provide a gas catalytic heater in which the slippage of fuel gas passed the porous catalytically active layer is significantly reduced.